X-ray tubes are used for X-ray image diagnosis, non-destructive inspection and the like. The X-ray tubes include a stationary anode type and a rotating anode type, which can be selected according to use. An X-ray tube comprises an anode target, a cathode and a vacuum envelope. The anode target is configured to emit X-ray by incidence of an electron beam.
The cathode comprises a filament coil and an electron converging cup. The filament coil is configured to emit electrons. A high tube voltage in the range of several tens to several hundreds of kilovolts (kV) is applied between the anode target and the cathode. In this manner, the electron converging cup can act an electron lens and converge an electron beam emitted towards the anode target. The electron converging cup comprises a trench portion in which the filament coil is accommodated. The trench portion comprises an upper inner circumferential wall and a lower inner circumferential wall located on an opposite side to the anode target with respect to the upper inner circumferential wall and having dimensions smaller than those of the upper inner circumferential wall.